From b968d4da48fd3b9ae703698bfe31ecdc731630fa Mon Sep 17 00:00:00 2001
From: Sathya Gunasekaran <gsathya.ceg@gmail.com>
Date: Wed, 16 Aug 2023 15:39:01 +0100
Subject: [PATCH] [hir] Validate globals are equal before propagating

Make sure the value of the globals in phi operands are the same before constant
propagating them.
---
 .../src/Optimization/ConstantPropagation.ts   | 13 ++++++++
 ...t-propagate-global-phis-constant.expect.md | 33 +++++++++++++++++++
 ...constant-propagate-global-phis-constant.js |  6 ++++
 3 files changed, 52 insertions(+)
 create mode 100644 compiler/forget/packages/babel-plugin-react-forget/src/__tests__/fixtures/compiler/constant-propagate-global-phis-constant.expect.md
 create mode 100644 compiler/forget/packages/babel-plugin-react-forget/src/__tests__/fixtures/compiler/constant-propagate-global-phis-constant.js

diff --git a/compiler/forget/packages/babel-plugin-react-forget/src/Optimization/ConstantPropagation.ts b/compiler/forget/packages/babel-plugin-react-forget/src/Optimization/ConstantPropagation.ts
index 8b7691ee1d..cba7623a45 100644
--- a/compiler/forget/packages/babel-plugin-react-forget/src/Optimization/ConstantPropagation.ts
+++ b/compiler/forget/packages/babel-plugin-react-forget/src/Optimization/ConstantPropagation.ts
@@ -206,6 +206,19 @@ function evaluatePhi(phi: Phi, constants: Constants): Constant | null {
         }
         break;
       }
+      case "LoadGlobal": {
+        CompilerError.invariant(value.kind === "LoadGlobal", {
+          reason: "value kind expected to be LoadGlobal",
+          loc: null,
+          suggestions: null,
+        });
+
+        // different global values, can't constant propogate
+        if (operandValue.name !== value.name) {
+          return null;
+        }
+        break;
+      }
       default:
         return null;
     }
diff --git a/compiler/forget/packages/babel-plugin-react-forget/src/__tests__/fixtures/compiler/constant-propagate-global-phis-constant.expect.md b/compiler/forget/packages/babel-plugin-react-forget/src/__tests__/fixtures/compiler/constant-propagate-global-phis-constant.expect.md
new file mode 100644
index 0000000000..5f8201c8f2
--- /dev/null
+++ b/compiler/forget/packages/babel-plugin-react-forget/src/__tests__/fixtures/compiler/constant-propagate-global-phis-constant.expect.md
@@ -0,0 +1,33 @@
+
+## Input
+
+```javascript
+function Test() {
+  const { tab } = useFoo();
+  const currentTab = tab === WAT ? WAT : WAT;
+
+  return <Foo value={currentTab} />;
+}
+
+```
+
+## Code
+
+```javascript
+import { unstable_useMemoCache as useMemoCache } from "react";
+function Test() {
+  const $ = useMemoCache(1);
+  const { tab } = useFoo();
+  tab === WAT ? WAT : WAT;
+  let t0;
+  if ($[0] === Symbol.for("react.memo_cache_sentinel")) {
+    t0 = <Foo value={WAT} />;
+    $[0] = t0;
+  } else {
+    t0 = $[0];
+  }
+  return t0;
+}
+
+```
+      
\ No newline at end of file
diff --git a/compiler/forget/packages/babel-plugin-react-forget/src/__tests__/fixtures/compiler/constant-propagate-global-phis-constant.js b/compiler/forget/packages/babel-plugin-react-forget/src/__tests__/fixtures/compiler/constant-propagate-global-phis-constant.js
new file mode 100644
index 0000000000..a9b0384026
--- /dev/null
+++ b/compiler/forget/packages/babel-plugin-react-forget/src/__tests__/fixtures/compiler/constant-propagate-global-phis-constant.js
@@ -0,0 +1,6 @@
+function Test() {
+  const { tab } = useFoo();
+  const currentTab = tab === WAT ? WAT : WAT;
+
+  return <Foo value={currentTab} />;
+}